JP2006322431A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of misfire in a cylinder in which an air fuel ratio of air fuel mixture is richer than a theoretical air-fuel ratio during sulfur poisoning recovery control. <P>SOLUTION: This exhaust emission control device for an internal combustion engine is provided with a plurality of cylinders #1 to #4, and the cylinders #1 to #4 are divided into at least two cylinder groups. Exhaust branch pipes 5, 6 are connected with the respective cylinder groups, and are jointed on the downstream side to be connected with one exhaust pipe 7. A NOx catalyst 10 is arranged inside the one common exhaust pipe 7. As sulfur poisoning recovery control of the NOx catalyst 10, exhaust gas at a rich air-fuel ratio is exhausted from one of the cylinder groups, and exhaust gas at a lean air-fuel ratio is exhausted from the other of the cylinder groups. During the sulfur poisoning recovery control, when gas including vapor is purged to an intake pipe 4 as purge gas, the purge gas amount is controlled in accordance with a vapor concentration in the purge gas, or a ratio of the purge gas amount with respect to fresh air amount flowing inside the intake pipe 4 is controlled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  As a catalyst for reducing and purifying nitrogen oxide (NOx) in exhaust gas discharged from an internal combustion engine, it absorbs NOx in exhaust gas when the air-fuel ratio of the exhaust gas flowing into it is leaner than the stoichiometric air-fuel ratio Or a catalyst of the type that reduces and purifies NOx retained when the air-fuel ratio of the exhaust gas flowing into it becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio (hereinafter referred to as “NOx catalyst”). ") Is known. An internal combustion engine equipped with such a NOx catalyst is disclosed in Patent Document 1.

  The internal combustion engine disclosed in Patent Document 1 includes six cylinders, and these cylinders are divided into two cylinder groups. An exhaust pipe (hereinafter referred to as “exhaust branch pipe”) is connected to each cylinder group, and these exhaust branch pipes merge downstream to form one common exhaust pipe (hereinafter referred to as “common exhaust pipe”). . A NOx catalyst is disposed in the common exhaust pipe.

  By the way, the exhaust gas contains sulfur oxide (SOx) in addition to NOx. When NOx is held in the NOx catalyst, SOx is also held in the NOx catalyst. Thus, if SOx is retained in the NOx catalyst (that is, the NOx catalyst is poisoned by the sulfur component), the amount of NOx that can be retained by the NOx catalyst is reduced accordingly. For this reason, in order to maintain the NOx retention capacity of the NOx catalyst as high as possible, it is necessary to remove SOx from the NOx catalyst. In order to remove SOx from the NOx catalyst (that is, to recover the NOx catalyst from poisoning by the sulfur component), the temperature of the NOx catalyst is raised to a temperature at which SOx can be removed, and flows into the NOx catalyst. It is necessary to make the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich (weakly rich).

  Therefore, in Patent Document 1, in order to remove SOx from the NOx catalyst, the following sulfur poisoning recovery control is performed. That is, the air-fuel ratio of exhaust gas discharged from one cylinder group is made rich, and the air-fuel ratio of exhaust gas discharged from the other cylinder group is made lean, and these rich air-fuel ratio exhaust gases (hereinafter referred to as “rich exhaust gas”) And a lean air-fuel ratio exhaust gas (hereinafter referred to as “lean exhaust gas”) are combined upstream of the NOx catalyst and then flowed into the NOx catalyst. Here, in Patent Document 1, when the rich exhaust gas and the lean exhaust gas are merged, the rich degree of the rich exhaust gas and the lean exhaust gas are set such that the total air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio. The lean degree of has been adjusted.

  According to this, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is the stoichiometric air-fuel ratio. Further, when the rich exhaust gas and the lean exhaust gas merge, the HC in the rich exhaust gas is in the lean exhaust gas. It reacts with oxygen, and the heat of reaction raises the temperature of the exhaust gas. As a result, the temperature of the NOx catalyst is raised. Thus, in Patent Document 1, the temperature of the NOx catalyst is raised to a temperature at which SOx can be removed, and exhaust gas having a stoichiometric air-fuel ratio is supplied to the NOx catalyst to remove SOx from the NOx catalyst. .

  By the way, an internal combustion engine having a charcoal canister (hereinafter simply referred to as “canister”) that adsorbs and holds evaporated fuel (hereinafter referred to as “vapor”) generated in a fuel tank is known. In such an internal combustion engine, vapor is discharged from the canister to the intake pipe during engine operation so that the activated carbon of the canister is not saturated with vapor.

JP 2004-68690 A Japanese Patent Laid-Open No. 11-343836 JP 2000-18025 A

  By the way, as described above, the vapor discharged to the intake pipe flows into each cylinder. Here, in the internal combustion engine described in Patent Document 1, when the vapor is discharged from the canister to the intake pipe during the sulfur poisoning recovery control, each cylinder is equivalent to the amount of vapor flowing from the canister to each cylinder. The amount of fuel inside increases. At this time, in particular, in the cylinder in which the air-fuel ratio of the air-fuel mixture is made richer than the stoichiometric air-fuel ratio in order to exhaust the rich air-fuel ratio exhaust gas during the sulfur poisoning recovery control, the amount of fuel in the cylinder is too large. As a result, misfire may occur in the cylinder.

  In view of such circumstances, the object of the present invention is to make the air-fuel ratio of the air-fuel mixture greater than the stoichiometric air-fuel ratio during the sulfur poisoning recovery control when the vapor is discharged from the canister to the intake pipe during the sulfur poisoning recovery control of the NOx catalyst. This is also to suppress the occurrence of misfire in the rich cylinder.

  In order to solve the above-mentioned problem, in the first invention, a plurality of cylinders are provided, these cylinders are divided into at least two cylinder groups, exhaust branch pipes are connected to the respective cylinder groups, and these exhaust branch pipes are connected to the downstream side. In the internal combustion engine connected to one common exhaust pipe, a NOx catalyst is disposed in the common one exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, Gas containing vapor during sulfur poisoning recovery control in an exhaust purification system that controls exhaust of rich air-fuel ratio from a cylinder group and exhaust of lean air-fuel ratio from the other cylinder group Is purged into the intake pipe as a purge gas, the purge gas quantity is controlled according to the vapor concentration in the purge gas, or the ratio of the purge gas quantity to the fresh air quantity flowing in the intake pipe is controlled.

  In the second invention, in the first invention, during the sulfur poisoning recovery control, when the gas containing vapor is purged to the intake pipe as purge gas, the vapor concentration in the purge gas is higher than a predetermined concentration. The purge gas amount is reduced or the ratio of the purge gas amount to the fresh air amount flowing in the intake pipe is reduced.

  In the third invention, in the first invention, during the sulfur poisoning recovery control, when the gas containing vapor is purged to the intake pipe as the purge gas, the purge gas amount is decreased as the vapor concentration in the purge gas is higher, or The ratio of the purge gas amount to the fresh air amount flowing in the intake pipe is reduced.

  In order to solve the above problems, in the fourth invention, a plurality of cylinders are provided, the cylinders are divided into at least two cylinder groups, exhaust branch pipes are connected to the respective cylinder groups, and the exhaust branch pipes are connected to the downstream side. In the internal combustion engine connected to one common exhaust pipe, a NOx catalyst is disposed in the common one exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, Gas containing vapor during sulfur poisoning recovery control in an exhaust purification system that controls exhaust of rich air-fuel ratio from a cylinder group and exhaust of lean air-fuel ratio from the other cylinder group Is purged into the intake pipe as a purge gas, the amount of purge gas is reduced when the richness of the air-fuel ratio of the cylinder that discharges the rich air-fuel ratio exhaust gas is greater than a predetermined richness. To or reduce the rate of the purge gas amount to the amount of fresh air flowing through the intake pipe.

  In the fifth aspect, in the fourth aspect, during the sulfur poisoning recovery control, when the gas containing vapor is purged to the intake pipe as a purge gas, the vapor concentration in the purge gas is higher than a predetermined concentration. The purge gas amount is reduced or the ratio of the purge gas amount to the fresh air amount flowing in the intake pipe is reduced.

  In order to solve the above-mentioned problem, in the sixth invention, a plurality of cylinders are provided, these cylinders are divided into two cylinder groups, exhaust branch pipes are connected to the respective cylinder groups, and these exhaust branch pipes are connected downstream. An exhaust gas purification apparatus for an internal combustion engine joined together and connected to a common exhaust pipe, wherein a NOx catalyst is disposed in the common exhaust pipe, and one cylinder is used as sulfur poisoning recovery control of the NOx catalyst. In an exhaust purification system that controls exhaust of a rich air-fuel ratio from a group and exhausts a lean air-fuel ratio from the other cylinder group, during a sulfur poisoning recovery control, the gas containing vapor is removed. When purging the intake pipe as purge gas, the purge gas amount is reduced as the air-fuel ratio rich degree of the cylinder that exhausts the rich air-fuel ratio exhaust gas is increased, or the amount of fresh air flowing in the intake pipe is reduced. To reduce the proportion of Jigasu amount.

  In the seventh invention, in the sixth invention, during the sulfur poisoning recovery control, when the gas containing vapor is purged to the intake pipe as the purge gas, the purge gas amount is decreased as the vapor concentration in the purge gas is higher, or The ratio of the purge gas amount to the fresh air amount flowing in the intake pipe is reduced.

  In order to solve the above-mentioned problem, in the eighth invention, a plurality of cylinders are provided, these cylinders are divided into at least two cylinder groups, exhaust branch pipes are connected to the respective cylinder groups, and these exhaust branch pipes are connected to the downstream side. In the internal combustion engine connected to one common exhaust pipe, a NOx catalyst is disposed in the common one exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, Gas containing vapor during sulfur poisoning recovery control in an exhaust purification system that controls exhaust of rich air-fuel ratio from a cylinder group and exhaust of lean air-fuel ratio from the other cylinder group When purging the intake pipe as a purge gas, the air-fuel ratio of each cylinder is controlled in accordance with the vapor concentration in the purge gas.

  In the ninth invention, in the eighth invention, during the sulfur poisoning recovery, when the gas containing the vapor is purged to the intake pipe as the purge gas, when the vapor concentration in the purge gas is higher than a predetermined concentration, it is rich. The richness of the air-fuel ratio of the cylinder that discharges the air-fuel ratio exhaust gas is reduced, and the leanness of the air-fuel ratio of the cylinder that discharges the lean air-fuel ratio exhaust gas is increased.

  In the tenth invention, in the eighth invention, when the gas containing vapor is purged into the intake pipe as purge gas during recovery from sulfur poisoning, the richer the air-fuel ratio exhaust gas is discharged, the higher the vapor concentration in the purge gas is. The richness of the air-fuel ratio of the cylinder to be reduced is reduced, and the leanness of the air-fuel ratio of the cylinder that discharges the exhaust gas having the lean air-fuel ratio is increased.

  In order to solve the above-mentioned problem, in the eleventh invention, a plurality of cylinders are provided, these cylinders are divided into two cylinder groups, exhaust branch pipes are connected to the respective cylinder groups, and these exhaust branch pipes are connected downstream. An exhaust gas purification apparatus for an internal combustion engine joined together and connected to a common exhaust pipe, wherein a NOx catalyst is disposed in the common exhaust pipe, and one cylinder is used as sulfur poisoning recovery control of the NOx catalyst. In an exhaust purification device that controls exhaust of rich air-fuel ratio from the group and exhaust of lean air-fuel ratio from the other cylinder group, the gas containing vapor is purged into the intake pipe as purge gas When the vapor concentration in the purge gas is higher than a predetermined concentration, the execution of the sulfur poisoning recovery control is prohibited.

  In the twelfth invention, in the eleventh invention, when the vapor concentration in the purge gas is higher than a predetermined concentration when the gas containing vapor is purged into the intake pipe as the purge gas, the sulfur poisoning recovery control is performed. While prohibiting the execution, the purge gas amount is increased or the ratio of the purge gas amount to the fresh air amount flowing in the intake pipe is increased.

  Generation of misfire in a cylinder in which the air-fuel ratio of the air-fuel mixture is made richer than the stoichiometric air-fuel ratio during sulfur poisoning recovery control when vapor is discharged from the canister to the intake pipe during sulfur poisoning recovery control of the NOx catalyst Is suppressed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an internal combustion engine equipped with the exhaust emission control device of the present invention. In FIG. 1, 1 indicates a main body of an internal combustion engine, and # 1 to # 4 indicate a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, respectively. Each cylinder is provided with fuel injection valves 21, 22, 23, 24 correspondingly. Each cylinder is connected to an intake pipe 4 via a corresponding intake branch pipe 3. Further, a first exhaust branch pipe 5 is connected to the first cylinder and the fourth cylinder, and a second exhaust branch pipe 6 is connected to the second cylinder and the third cylinder. That is, when the first cylinder and the fourth cylinder are collectively referred to as a first cylinder group, and the second cylinder and the third cylinder are collectively referred to as a second cylinder group, the first cylinder group includes the first cylinder group. An exhaust branch pipe 5 is connected, and a second exhaust branch pipe 6 is connected to the second cylinder group. These exhaust branch pipes 5 and 6 merge on the downstream side and are connected to a common exhaust pipe 7.

  The first exhaust branch pipe 5 is one exhaust branch pipe on the downstream side, but is branched into two on the upstream side, and the exhaust branch pipes branched into these two are the first cylinder and the first cylinder, respectively. It is connected to 4 cylinders. Similarly, the second exhaust branch pipe 6 is also one exhaust branch pipe on the downstream side, but is branched into two on the upstream side, and the two exhaust branch pipes branched into the second cylinder and the second branch branch pipe, respectively. Connected to the third cylinder. In the following description, when a portion divided into two on the upstream side of the exhaust branch pipes 5 and 6 is specified and expressed, this is expressed as “a branch portion of the exhaust branch pipe”, and the exhaust branch pipes 5 and 6 are expressed. In the case where one portion on the downstream side is specified and expressed, this is expressed as “a collection portion of exhaust branch pipes”.

  Three-way catalysts 8 and 9 are disposed in the gathering portions of the exhaust branch pipes 5 and 6, respectively, and a NOx catalyst 10 is disposed in the exhaust pipe 7. In addition, air-fuel ratio sensors 11 and 12 are arranged at the collection portions of the exhaust branch pipes 5 and 6 upstream of the three-way catalysts 5 and 6, respectively. Air-fuel ratio sensors 13 and 14 are also disposed in the exhaust pipe 7 upstream and downstream of the NOx catalyst 10, respectively.

  As shown in FIG. 2, the three-way catalysts 8 and 9 have a temperature equal to or higher than a certain temperature (so-called activation temperature), and the air-fuel ratio of the exhaust gas flowing into the three-way catalysts 8 and 9 is the stoichiometric air-fuel ratio. When in the vicinity (in the region X of FIG. 2), nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) in the exhaust gas are simultaneously purified at a high purification rate. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is leaner than the stoichiometric air-fuel ratio, the three-way catalyst absorbs oxygen in the exhaust gas, and the air-fuel ratio of the exhaust gas flowing into the exhaust gas is greater than the stoichiometric air-fuel ratio. When it is also rich, it has an oxygen absorption / release capability of releasing absorbed oxygen. As long as this oxygen absorption / release capability functions normally, the air / fuel ratio of the exhaust gas flowing in is leaner or richer than the stoichiometric air / fuel ratio. Therefore, NOx, CO, and HC in the exhaust gas are simultaneously purified with a high purification rate.

  The NOx catalyst 10 has an exhaust gas when its temperature is higher than a certain temperature (so-called activation temperature) and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is leaner (larger) than the stoichiometric air-fuel ratio. It is retained by absorbing or storing NOx therein, and when the air-fuel ratio of the exhaust gas flowing therein becomes richer than the stoichiometric air-fuel ratio or stoichiometric air-fuel ratio, the retained NOx is reduced and purified.

  By the way, if SOx is contained in the exhaust gas under the condition in which NOx is held in the NOx catalyst 10, this SOx is also held in the NOx catalyst. As described above, when SOx is held in the NOx catalyst, the amount of NOx that can be held by the NOx catalyst is reduced accordingly. For this reason, in order to maintain the NOx retention capacity of the NOx catalyst as high as possible, it is necessary to remove SOx from the NOx catalyst. Here, if the exhaust gas having a stoichiometric air-fuel ratio or rich (preferably, very close to the stoichiometric air-fuel ratio) is supplied to the NOx catalyst while the temperature of the NOx catalyst is set to a temperature at which SOx can be removed, the NOx catalyst SOx can be removed. In other words, it can be said that the NOx catalyst of the present embodiment releases SOx when the stoichiometric or rich air-fuel ratio exhaust gas is supplied to the NOx catalyst in a state where the temperature is set to a certain temperature.

  Therefore, when it is required to remove SOx from the NOx catalyst 10, in the present embodiment, the following sulfur poisoning recovery control is executed, so that the temperature of the NOx catalyst is set to a temperature at which SOx can be removed and NOx. An exhaust gas having a stoichiometric or rich air-fuel ratio is supplied to the catalyst. That is, in the sulfur poisoning recovery control of the present embodiment, rich air-fuel ratio exhaust gas (hereinafter referred to as “rich exhaust gas”) is discharged from the first cylinder and the fourth cylinder (that is, the first cylinder group) and the first. The air-fuel ratio of the air-fuel mixture (hereinafter referred to as “lean exhaust gas”) filled in each cylinder so that the exhaust gas having a lean air-fuel ratio (hereinafter referred to as “lean exhaust gas”) is discharged from the second cylinder and the third cylinder (that is, the second cylinder group). (Also referred to as “engine air-fuel ratio”).

  Here, the richness of the rich exhaust gas discharged from each cylinder and the leanness of the lean exhaust gas are determined when the rich exhaust gas and the lean exhaust gas are mixed upstream of the NOx catalyst 10 and flow into the NOx catalyst. The air-fuel ratio of the exhaust gas is adjusted so as to be the stoichiometric air-fuel ratio or a desired rich air-fuel ratio.

  Generally, the temperature at which SOx can be removed from the NOx catalyst 10 (hereinafter referred to as “the temperature at which SOx can be removed”) is higher than the temperature at which the NOx catalyst holds NOx or purifies NOx, so that SOx is removed from the NOx catalyst. In order to remove it, it is necessary to raise the temperature of the NOx catalyst. In this regard, according to the sulfur poisoning recovery control of the present embodiment, the rich exhaust gas and the lean exhaust gas are mixed and the HC in the rich exhaust gas reacts with the oxygen in the lean exhaust gas, so that the reaction heat This reaction heat can raise the temperature of the NOx catalyst to a temperature at which SOx can be removed.

  As described above, in order to remove SOx from the NOx catalyst 10, it is necessary to set the air-fuel ratio of the exhaust gas flowing into the NOx catalyst to the stoichiometric air-fuel ratio or the rich air-fuel ratio. In this regard, according to the sulfur poisoning recovery control of the present embodiment, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is the stoichiometric air-fuel ratio or the rich air-fuel ratio. Thus, according to the sulfur poisoning recovery control of the present embodiment, SOx can be removed from the NOx catalyst 10.

  Note that the air-fuel ratio of the rich exhaust gas discharged from each cylinder in the sulfur poisoning recovery control is preferably a rich air-fuel ratio close to the stoichiometric air-fuel ratio. Therefore, the lean exhaust gas discharged from each cylinder in the sulfur poisoning recovery control. The air / fuel ratio of the gas is also preferably a lean air / fuel ratio close to the stoichiometric air / fuel ratio.

  Incidentally, as the air-fuel ratio sensor, for example, there is a so-called linear air-fuel ratio sensor that outputs a current with the characteristics shown in FIG. This linear air-fuel ratio sensor outputs a current of 0 A when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, and outputs a current of 0 A or less that is larger as the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio. As the air-fuel ratio of the exhaust gas becomes leaner than the stoichiometric air-fuel ratio, a larger current of 0 A or more is output. That is, the linear air-fuel ratio sensor outputs a current that changes linearly according to the air-fuel ratio of the exhaust gas.

As another air-fuel ratio sensor, for example, there is a so-called O ₂ sensor that outputs a voltage with the characteristics shown in FIG. This O ₂ sensor outputs a voltage of approximately 0 V when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and outputs a voltage of approximately 1 V when it is richer than the stoichiometric air-fuel ratio. The output voltage rapidly changes in a region where the air-fuel ratio of the exhaust gas is in the vicinity of the theoretical air-fuel ratio and crosses 0.5V. That is, the O ₂ sensor outputs a constant voltage that varies depending on whether the air-fuel ratio of the exhaust gas is lean or rich with respect to the stoichiometric air-fuel ratio.

By the way, in the embodiment of the present invention, a linear air-fuel ratio sensor is employed as the air-fuel ratio sensors 11 and 12 upstream of the three-way catalysts 8 and 9 and the air-fuel ratio sensor 13 between the three-way catalyst and the NOx catalyst 10, and the NOx An O ₂ sensor is employed as the air-fuel ratio sensor 14 downstream of the catalyst. In this embodiment, the air-fuel ratio of the air-fuel mixture filled in each cylinder is controlled to the target air-fuel ratio based on the outputs from these sensors. Next, as an example of such air-fuel ratio control, the control of the present embodiment for controlling the air-fuel ratio of the air-fuel mixture charged in each cylinder to the stoichiometric air-fuel ratio during normal operation (hereinafter referred to as “normal stoichiometric control”) will be described. .

  First, the outline of the normal stoichiometric control of this embodiment will be described. The air-fuel ratio sensors (hereinafter referred to as “linear air-fuel ratio sensors”) 11 and 12 upstream of the three-way catalysts 8 and 9 indicate that the air-fuel ratio of the exhaust gas (hereinafter referred to as “exhaust air-fuel ratio”) is leaner than the stoichiometric air-fuel ratio. In the illustrated case, since the air-fuel ratio (engine air-fuel ratio) of the air-fuel mixture filled in the corresponding cylinder is leaner than the stoichiometric air-fuel ratio, fuel injection is performed so that the engine air-fuel ratio in the corresponding cylinder approaches the stoichiometric air-fuel ratio. The amount of fuel injected from the valve (hereinafter referred to as “fuel injection amount”) is increased. Conversely, when the linear air-fuel ratio sensors 11 and 12 indicate that the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio, the fuel injection amount is reduced so that the engine air-fuel ratio in the corresponding cylinder approaches the stoichiometric air-fuel ratio. Is done.

  By controlling the fuel injection amount in this way, basically, the engine air-fuel ratio should be controlled to the stoichiometric air-fuel ratio. However, if the linear air-fuel ratio sensors 11 and 12 have an output error, the engine air-fuel ratio is not controlled to the stoichiometric air-fuel ratio. For example, if the linear air-fuel ratio sensor tends to output a current value corresponding to the air-fuel ratio that is shifted to a richer side than the current value corresponding to the actual exhaust air-fuel ratio, the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. Even if this is the case, the exhaust air-fuel ratio will be richer than the stoichiometric air-fuel ratio. For this reason, the fuel injection amount is reduced, and as a result, the engine air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. On the other hand, if the linear air-fuel ratio sensor tends to output a current value corresponding to the air-fuel ratio that deviates to a leaner side than the current value corresponding to the actual exhaust air-fuel ratio, the engine air-fuel ratio is less than the stoichiometric air-fuel ratio. Is also richly controlled.

Therefore, in the present embodiment, such output errors of the linear air-fuel ratio sensors 11 and 12 are compensated using the output value of the O ₂ sensor 14 downstream of the NOx catalyst 10. That is, if the linear air-fuel ratio sensor has no output error and the engine air-fuel ratio is controlled to the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst should be the stoichiometric air-fuel ratio. The O ₂ sensor outputs 0.5 V (hereinafter referred to as “reference voltage value”) corresponding to the theoretical air-fuel ratio.

However, if there is an output error in the linear air-fuel ratio sensors 11 and 12 and the engine air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, for example, the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst 10 is the stoichiometric air-fuel ratio. It is richer than. At this time, the O ₂ sensor 14 outputs a voltage value corresponding to an air-fuel ratio richer than the theoretical air-fuel ratio. Here, the difference between the voltage value output from the O ₂ sensor at this time and the reference voltage value indicates an output error of the linear air-fuel ratio sensor. Therefore, in this embodiment, the output of the linear air-fuel ratio sensor is compensated so that the output error of the linear air-fuel ratio sensor is compensated based on the difference between the voltage value actually output from the O ₂ sensor and the reference voltage value. Correct the current value.

Conversely, when the linear air-fuel ratio sensors 11 and 12 have an output error and the engine air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio, the voltage value output from the O ₂ sensor 14 and the reference voltage value Based on the difference, the output current value of the linear air-fuel ratio sensor is corrected so that the output error of the lean air-fuel ratio sensor is compensated.

Next, the normal stoichiometric control of this embodiment will be described as a more specific example. In the present embodiment, the valve opening time (hereinafter referred to as “reference valve opening time”) of the fuel injection valve that is a reference for setting the engine air-fuel ratio to the stoichiometric air-fuel ratio is determined according to the following equation 1.
TAUB = α × Ga / Ne (1)
Here, α is a constant, Ga is the intake air amount (the amount of air taken into the cylinder), and Ne is the engine speed. That is, according to the present embodiment, the reference valve opening time is calculated based on the intake air amount per unit engine speed, and tends to become longer as the intake air amount per unit engine speed increases.

Then, the actual valve opening time (hereinafter referred to as “actual valve opening time”) TAU of the fuel injection valve is calculated according to the following equation 2.
TAU = TAUB × F1 × β × γ (2)
Here, F1 is a correction coefficient (hereinafter also referred to as “main correction coefficient”) obtained as described later, and β and γ are constants determined according to the engine operating state.

The main correction coefficient F1 is calculated according to the following equation 3.
F1 = Kp1 × (I−F2−I ₀ ) + Ki1 × ∫ (I−F2−I ₀ ) dt + Kd1 × d (I−F2−I ₀ ) / dt (3)
Here, I ₀ is a current value to be output from the linear air-fuel ratio sensors 11 and 12 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, and I is actually output from the linear air-fuel ratio sensors 11 and 12. F2 is a correction coefficient (hereinafter also referred to as “sub-correction coefficient”) obtained as described later, Kp1 is a proportional gain, Ki1 is an integral gain, and Kd1 is a differential gain. . That is, according to this, the main correction coefficient F1 is PID-controlled.

On the other hand, the sub correction coefficient F2 is calculated according to the following equation 4.
_{F2 = Kp2 × (V 0 -V} ) + Ki2 × ∫ (V 0 -V) dt + Kd2 × d (V 0 -V) / dt ... (4)
Here, V ₀ is a voltage value that should be output from the O ₂ sensor 14 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, V is a voltage value that is actually output from the O ₂ sensor 14, Kp2 is a proportional gain, Ki2 is an integral gain, and Kd2 is a differential gain. That is, according to this, the sub correction coefficient F2 is also PID-controlled.

  Thus, according to this embodiment, the engine air-fuel ratio is maintained at the stoichiometric air-fuel ratio.

  By the way, in the embodiment of the present invention, during the sulfur poisoning recovery control, the richness or leanness of the engine air-fuel ratio in each cylinder group is set so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 becomes a predetermined air-fuel ratio. Is controlled to control the richness or leanness of the exhaust gas discharged from each cylinder group. Next, regarding the control of the engine air-fuel ratio in each cylinder group during the sulfur poisoning recovery control (hereinafter also referred to as “sulfur poisoning recovery air-fuel ratio control”), the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to the stoichiometric air-fuel ratio. An example will be described.

  First, an outline of the sulfur poisoning recovery air-fuel ratio control of the present embodiment will be described. In the present embodiment, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is controlled to the stoichiometric air-fuel ratio during the sulfur poisoning recovery control, the fuel injection amount (reference) for setting the engine air-fuel ratio to the stoichiometric air-fuel ratio. (Hereinafter referred to as “reference fuel injection amount”) is increased by a predetermined amount in one cylinder group and decreased by the same amount as the predetermined amount in the other cylinder group. As a result, exhaust gas having a rich air-fuel ratio is exhausted from one cylinder group and exhaust gas having a lean air-fuel ratio is exhausted from the other cylinder group. In theory, the exhaust gas flowing into the NOx catalyst is emptied. The fuel ratio becomes the stoichiometric air fuel ratio.

  In practice, however, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 often does not become the stoichiometric air-fuel ratio for reasons such as variations in fuel injector performance. Here, for example, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is richer than the stoichiometric air-fuel ratio, the linear air-fuel ratio sensor 13 outputs a current value corresponding to the rich air-fuel ratio. Therefore, in the present embodiment, when the linear air-fuel ratio sensor outputs a current value corresponding to the rich air-fuel ratio, the fuel injection amount in the cylinder performing combustion at the rich air-fuel ratio is reduced, or the lean air-fuel ratio is reduced. By reducing the fuel injection amount in the cylinder that is performing the combustion in the above or by combining them, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst approaches the stoichiometric air-fuel ratio.

  Conversely, when the linear air-fuel ratio sensor 13 outputs a current value corresponding to the lean air-fuel ratio, the fuel injection amount in the cylinder that performs combustion at the rich air-fuel ratio is increased, or combustion is performed at the lean air-fuel ratio. The air injection ratio of the exhaust gas flowing into the NOx catalyst 10 is made closer to the stoichiometric air fuel ratio by increasing the fuel injection amount in the cylinder being performed or combining them.

  Thus, when the fuel injection amount in each cylinder is controlled, if there is no output error in the linear air-fuel ratio sensor 13, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is controlled to the stoichiometric air-fuel ratio. However, if there is an output error in the linear air-fuel ratio sensor, for example, if the linear air-fuel ratio sensor tends to output a current value corresponding to a richer air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is theoretically It will be controlled leaner than the air-fuel ratio. Conversely, if the linear air-fuel ratio sensor tends to output a current value corresponding to the leaner air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst will be controlled to be richer than the stoichiometric air-fuel ratio. become.

Here, for example, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is richer than the stoichiometric air-fuel ratio, the O ₂ sensor 14 detects the reference voltage value (O.sub.2 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio). _The voltage value corresponding to the air-fuel ratio on the richer side than the voltage value output by the _two sensors) is output. The difference between the voltage value actually output by the O ₂ sensor and the reference voltage value indicates the output error of the linear air-fuel ratio sensor 13. Therefore, in this embodiment, the output of the linear air-fuel ratio sensor is compensated so that the output error of the linear air-fuel ratio sensor is compensated based on the difference between the voltage value actually output from the O ₂ sensor and the reference voltage value. Correct the current value.

Conversely, even when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is leaner than the stoichiometric air-fuel ratio, based on the difference between the voltage value actually output from the O ₂ sensor 14 and the reference voltage value, The output current value of the linear air-fuel ratio sensor is corrected so that the output error of the linear air-fuel ratio sensor 13 is compensated.

Next, the sulfur poisoning recovery air-fuel ratio control of this embodiment will be described more specifically. In the present embodiment, the reference valve opening time (the fuel injection valve opening time used as a reference for setting the engine air-fuel ratio to the stoichiometric air-fuel ratio) is determined according to the following equation (5).
TAUB = α × Ga / Ne (5)
This equation 5 is the same as the above equation 1, α is a constant, Ga is the intake air amount, and Ne is the engine speed.

Then, the actual valve opening time (actual valve opening time of the fuel injection valve) TAUR in the cylinder that performs combustion at the rich air-fuel ratio is calculated according to the following equation 6, and the actual valve opening time in the cylinder that performs combustion at the lean air-fuel ratio. TAUL is calculated according to the following equation 7.
TAUR = TAUB × R × F3 × β × γ (6)
TAUL = TAUB × L × F3 × β × γ (7)
Here, R is a value larger than 1 and a constant for extending the reference valve opening time so that the fuel injection amount increases, and L is a value smaller than 1 and the fuel injection amount decreases. Is a constant for shortening the reference valve opening time, F3 is a correction coefficient obtained as described later (hereinafter also referred to as “sulfur poisoning recovery main correction coefficient”), and β and γ are engine operations, respectively. It is a constant determined according to the state.

The sulfur recovery poisoning main correction coefficient F3 is calculated according to the following equation 8.
F3 = Kp3 × (I−F4−I ₀ ) + Ki3 × ∫ (I−F4−I ₀ ) dt + Kd3 × d (I−F4−I ₀ ) / dt (8)
Here, I ₀ is a current value that should be output from the linear air-fuel ratio sensor 13 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, and I is a current value that is actually output from the linear air-fuel ratio sensor 13. F4 is a correction coefficient obtained as described later (hereinafter also referred to as “sulfur poisoning recovery sub-correction coefficient”), Kp3 is a proportional gain, Ki3 is an integral gain, and Kd3 is a differential gain. . That is, according to this, the sulfur poisoning recovery main correction coefficient F1 is PID-controlled.

On the other hand, the sulfur poisoning recovery sub correction coefficient F4 is calculated according to the following equation 9.
_{F4 = Kp4 × (V 0 -V} ) + Ki4 × ∫ (V 0 -V) dt + Kd4 × d (V 0 -V) / dt ... (9)
Here, V ₀ is a voltage value that should be output from the O ₂ sensor 14 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, V is a voltage value that is actually output from the O ₂ sensor 14, Kp4 is a proportional gain, Ki4 is an integral gain, and Kd4 is a differential gain. That is, according to this, the sulfur poisoning recovery sub correction coefficient F4 is also PID-controlled.

  Thus, according to the present embodiment, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 is maintained at the stoichiometric air-fuel ratio during the sulfur poisoning recovery control.

  Incidentally, as shown in FIG. 1, the internal combustion engine of the present embodiment includes a charcoal canister 32 that contains activated carbon 31 for adsorbing and holding vapor (evaporated fuel) generated in the fuel tank 30. An internal space 33 of the canister 32 on one side of the activated carbon 31 communicates with the inside of the fuel tank 30 through the vapor passage 34 and can communicate with the intake pipe 4 downstream of the throttle valve 36 through the purge passage 35. It is said that. A purge control valve 37 for adjusting the flow passage area of the purge passage 35 is disposed in the purge passage 35. When the purge control valve 37 is opened, the internal space 33 of the canister 32 is communicated with the intake pipe 4 via the purge passage. In addition, the internal space 38 of the canister 32 on the other side of the activated carbon 31 is communicated with the atmosphere via the atmosphere tube 39.

  As described above, the vapor generated in the fuel tank 30 is adsorbed and held by the activated carbon 31 of the canister 32. However, since the amount of vapor that can be adsorbed and held by the activated carbon 31 is limited, the activated carbon 31 Before being saturated with vapor, the vapor must be removed from the activated carbon 31. Therefore, in the present embodiment, when a certain predetermined condition is satisfied during engine operation (when the internal combustion engine is operated), the purge control valve 37 is opened and the vapor of the activated carbon 31 is passed through the purge passage 35. To the intake pipe 4.

  That is, during engine operation, negative pressure (hereinafter referred to as “intake pipe negative pressure”) is generated in the intake pipe 4 downstream of the throttle valve 36. Therefore, when the purge control valve 37 is opened, intake pipe negative pressure is introduced into the canister 32 via the purge passage 35. The introduced intake pipe negative pressure causes air in the atmosphere to be sucked into the canister 32 through the atmosphere pipe 39, and the sucked air is sucked into the intake pipe 4 through the purge passage 35. At this time, the vapor adsorbed and held by the activated carbon 31 rides on the air passing through the canister 32 and is introduced into the intake pipe 4. In the present embodiment, for example, during normal stoichiometric control, the purge control valve 37 is opened to introduce vapor from the canister 32 to the intake pipe. Next, the control of the purge control valve 37 during the normal stoichiometric control will be described in detail.

  In the present embodiment, the purge rate during normal stoichiometric control is set in advance according to the engine operating state, in particular, the engine speed and the required torque. Here, the purge rate refers to the air and vapor purged from the purge passage 35 to the intake pipe 4 with respect to the amount of air (new air) sucked into each cylinder from the upstream of the throttle valve 36 (hereinafter referred to as “new air amount”). The ratio of the amount of the mixed gas (hereinafter referred to as “purge gas”). That is, in the present embodiment, during normal stoichiometric control, the ratio of purge gas to the fresh air amount (purge rate) is set according to the engine speed and the required torque, and the purge rate is set so that this set purge rate is achieved. The opening degree of the control valve 37 is controlled. Here, if the amount of fresh air is constant, the purge rate increases as the opening of the purge control valve 37 is increased.

  In this case, for example, as shown in FIG. 5, a purge rate map having a function of the engine speed N and the required torque T is prepared, and the purge rate is read by reading the purge rate from this map. A rate is set, a calculation formula is prepared instead of this map, and the purge rate is set by calculating the purge rate from this formula.

  Further, when the purge gas is introduced into the intake pipe 4 during normal stoichiometric control, the amount of fuel supplied to each cylinder is increased by the amount of vapor contained in the purge gas, and the air-fuel ratio of the air-fuel mixture charged in each cylinder is increased. (Engine air-fuel ratio) deviates from the stoichiometric air-fuel ratio, but this deviation is eliminated by air-fuel ratio control using the air-fuel ratio sensors 11, 12, and 14, as described above.

  By the way, in this embodiment, the purge control valve 37 is opened even during the above-described sulfur poisoning recovery control, and vapor is introduced from the canister 32 to the intake pipe 4. Next, the control of the purge control valve 37 during the sulfur poisoning recovery control will be described.

  In the first embodiment of the control of the purge control valve 37 during the sulfur poisoning recovery control, the vapor concentration in the purge gas is obtained during the normal stoichiometric control. Then, the purge rate during the sulfur poisoning recovery control is set according to the vapor concentration in the purge gas. More specifically, when the vapor concentration in the purge gas is higher than the predetermined concentration, the purge rate is set to be small, and when the vapor concentration in the purge gas is lower than the predetermined concentration, the purge rate is set to be high, or The higher the vapor concentration in the purge gas, the smaller the purge rate. Then, the opening degree of the purge control valve 37 is controlled so that the purge rate thus set is achieved.

  Thus, setting the purge rate during the sulfur poisoning recovery control according to the vapor concentration in the purge gas is advantageous from the viewpoint of suppressing the occurrence of misfire in the rich cylinder. That is, when vapor is supplied to the rich cylinder during the sulfur poisoning recovery control, the fuel injection amount of the rich cylinder is reduced by the air-fuel ratio control described above, and the occurrence of misfire in the rich cylinder may be suppressed. However, the fuel injection amount of the rich cylinder is not necessarily reduced. For example, only the fuel injection amount of the lean cylinder may be reduced. In such a case, there is too much fuel in the rich cylinder and misfire occurs. According to this embodiment, when the vapor concentration in the purge gas is high, that is, when the amount of vapor supplied to the rich cylinder is expected to be large, the amount of vapor supplied to the rich cylinder with the purge rate reduced is reduced. As a result, the occurrence of misfire in the rich cylinder is more reliably suppressed.

  Of course, in this embodiment, as a parameter used for setting the purge rate during the sulfur poisoning recovery control, the engine operating state (particularly, the engine speed and the required torque) may be added in addition to the vapor concentration.

  In this embodiment, for example, a map of the purge rate as a function of the vapor concentration or a map of the purge rate as a function of the vapor concentration, the engine speed, and the required torque is prepared in advance. The purge rate is set by reading the purge rate, or a calculation formula is prepared instead of this map, and the purge rate is set by calculating the purge rate from this calculation formula.

  Further, the purge rate during the sulfur poisoning recovery control may be set by correcting the purge rate set for the normal stoichiometric control according to the engine operating state according to the vapor concentration in the purge gas. In this case, more specifically, the purge rate is set according to the engine operating state (particularly, the engine speed and the required torque) as in the normal stoichiometric control. When the vapor concentration in the purge gas is lower than the predetermined concentration, the purge rate during the sulfur poisoning recovery control is set to the set purge rate, and when the vapor concentration in the purge gas is higher than the predetermined concentration. The purge rate during the sulfur poisoning recovery control is set to a purge rate smaller than the purge rate set above, or the purge rate during the sulfur poisoning recovery control is increased as the vapor concentration in the purge gas increases. The purge rate is smaller than the rate.

  In the above-described embodiment, the purge rate is changed according to the vapor concentration during the sulfur poisoning recovery control. However, the purge gas amount may be changed according to the vapor concentration. In this case, more specifically, during the sulfur poisoning recovery control, when the vapor concentration in the purge gas is higher than the predetermined concentration, the amount of purge gas is set to be small and the vapor concentration in the purge gas is lower than the predetermined concentration. Is set to a larger purge gas amount or a smaller purge gas amount as the vapor concentration in the purge gas is higher. Alternatively, during normal stoichiometric control, if the purge gas amount is set instead of the purge rate according to the engine operating state (especially engine speed and required torque), the engine operation is the same as during normal stoichiometric control. The purge gas amount is set according to the state, and when the vapor concentration in the purge gas is lower than the predetermined concentration during the sulfur poisoning recovery control, the purge gas amount during the sulfur poisoning recovery control is set to the set purge gas amount. When the vapor concentration in the purge gas is higher than the predetermined concentration, the purge gas amount during the sulfur poisoning recovery control is made smaller than the set purge gas amount, or the higher the vapor concentration in the purge gas, the higher the sulfur concentration is. The purge gas amount during the poisoning recovery control is set to an amount smaller than the set purge gas amount.

  When the purge gas is introduced into the intake pipe 4 during the sulfur poisoning recovery control, the amount of fuel supplied to each cylinder is increased by the amount of vapor contained in the purge gas, and the amount of the air-fuel mixture filled in each cylinder increases. Although the air-fuel ratio (engine air-fuel ratio) deviates from a predetermined air-fuel ratio, this deviation is eliminated by air-fuel ratio control using the air-fuel ratio sensors 13 and 14 as described above.

  FIG. 6 shows an example of a routine for controlling the purge control valve 37 according to the first embodiment. In the routine of FIG. 6, first, at step 10, it is judged if execution of sulfur poisoning recovery control is requested. Here, if execution of sulfur poisoning recovery control is not requested, the routine ends as it is. On the other hand, when the execution of the sulfur poisoning recovery control is requested, in step 11, the vapor concentration in the purge gas obtained during the normal stoichiometric control is read. Next, in step 12, the purge rate is set based on the vapor concentration read in step 11 as described in connection with the first embodiment. In step 13, the opening degree of the purge control valve 37 is controlled so that the purge rate set in step 12 is achieved.

  Next, a second embodiment of the control of the purge control valve 37 during the sulfur poisoning recovery control will be described. In the present embodiment, the purge rate is set according to the richness of the air-fuel ratio of the cylinder (hereinafter referred to as “rich cylinder”) that discharges the rich air-fuel ratio exhaust gas during the sulfur poisoning recovery control. More specifically, when the rich degree of the air-fuel ratio of the rich cylinder is larger than the predetermined degree, the purge rate is set to be small, and when the rich degree of the air-fuel ratio of the rich cylinder is smaller than the predetermined degree, the large purge is performed. Or a purge rate that decreases as the richness of the air-fuel ratio of the rich cylinder increases. Then, the opening degree of the purge control valve 37 is controlled so that the purge rate thus set is achieved.

  Thus, setting the purge rate during the sulfur poisoning recovery control according to the richness of the air-fuel ratio of the rich cylinder during the sulfur poisoning recovery control is also advantageous from the viewpoint of suppressing the occurrence of misfire in the rich cylinder. It is. That is, in this embodiment, the richness of the air-fuel ratio of the rich cylinder is large. At this time, if the vapor is supplied by supplying purge gas to the rich cylinder, the amount of fuel in the rich cylinder becomes too large and misfire occurs. When it is predicted that the purge rate will be reduced, the amount of vapor supplied to the rich cylinder is reduced. For this reason, generation | occurrence | production of the misfire in a rich cylinder is suppressed more reliably.

  Of course, in this embodiment, as a parameter used for setting the purge rate during the sulfur poisoning recovery control, in addition to the richness of the air-fuel ratio of the rich cylinder, the engine operating state (in particular, the engine speed and the required torque). May be added.

  In such an embodiment, for example, a map of the purge rate as a function of the richness of the air-fuel ratio of the rich cylinder, or a map of the richness of the air-fuel ratio of the rich cylinder, the engine speed and the required torque as a function. Prepare in advance and set the purge rate by reading the purge rate from this map, or prepare a calculation formula instead of this map and set the purge rate by calculating the purge rate from this formula To do.

  Further, the purge rate during the sulfur poisoning recovery control may be set according to the richness of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas. In this case, more specifically, regarding the rich degree of the air-fuel ratio of the rich cylinder, during the sulfur poisoning recovery control, the purge rate is set as described above, and regarding the vapor concentration in the purge gas, the vapor concentration in the purge gas is set. When the gas concentration is higher than the predetermined concentration, the purge rate is set to be small, and when the vapor concentration in the purge gas is lower than the predetermined concentration, the purge rate is set to be large, or the higher the vapor concentration in the purge gas is, the smaller the purge rate is. To do.

  In this case as well, as parameters used for setting the purge rate during the sulfur poisoning recovery control, in addition to the rich degree of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas, the engine operating state (particularly, Engine speed and required torque) may be added.

  In such an embodiment, for example, a purge rate map as a function of the richness of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas, or the richness of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas Prepare a map of the purge rate as a function of the engine speed and the required torque and set the purge rate by reading the purge rate from this map, or prepare a calculation formula instead of this map. The purge rate is set by calculating the purge rate from this formula.

  Further, the purge rate during the sulfur poisoning recovery control may be set by correcting the purge rate set for the normal stoichiometric control according to the engine operating state according to the rich degree of the air-fuel ratio of the rich cylinder. In this case, more specifically, the purge rate is set according to the engine operating state (particularly, the engine speed and the required torque) as in the normal stoichiometric control. If the rich degree of the air-fuel ratio of the rich cylinder is smaller than the predetermined degree, the purge rate during the sulfur poisoning recovery control is set to the set purge rate, and the rich degree of the air-fuel ratio of the rich cylinder is the predetermined degree. If it is greater than the above-mentioned degree, the purge rate during the sulfur poisoning recovery control is set to a purge rate smaller than the above-described purge rate, or the higher the richness of the air-fuel ratio of the rich cylinder, the higher the sulfur poisoning recovery. The purge rate under control is set to a purge rate smaller than the set purge rate.

  Of course, even in this case, the sulfur poisoning recovery is achieved by correcting the purge rate set for normal stoichiometric control according to the engine operating state according to the rich degree of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas. A purge rate during control may be set. In this case, more specifically, regarding the rich degree of the air-fuel ratio of the rich cylinder, during the sulfur poisoning recovery control, the purge rate is set as described above, and regarding the vapor concentration in the purge gas, the vapor concentration in the purge gas is set. Is lower than the predetermined concentration, the purge rate set according to the engine operating state (especially the engine speed and required torque) is set as the purge rate during the sulfur poisoning recovery control as in the normal stoichiometric control. When the vapor concentration in the purge gas is higher than the predetermined concentration, the purge rate during the sulfur poisoning recovery control is set to a purge rate smaller than the set purge rate, or the higher the vapor concentration in the purge gas is, The purge rate during the sulfur poisoning recovery control is set to a purge rate smaller than the set purge rate.

  In the above-described embodiment, the purge rate during the sulfur poisoning recovery control is changed according to the rich degree of the air-fuel ratio of the rich cylinder, but the sulfur poisoning recovery control is changed according to the rich degree of the air-fuel ratio of the rich cylinder. The amount of purge gas inside may be changed. In this case, more specifically, during the sulfur poisoning recovery control, if the rich degree of the air-fuel ratio of the rich cylinder is larger than the predetermined degree, the purge gas amount is reduced and the rich degree of the air-fuel ratio of the rich cylinder is When it is smaller than the predetermined degree, the purge gas amount is increased, or the purge gas amount is decreased as the richness of the air-fuel ratio of the rich cylinder is increased.

  Of course, in this case as well, the purge gas amount during the sulfur poisoning recovery control may be changed according to the richness of the air-fuel ratio of the rich cylinder and the vapor concentration in the purge gas. In this case, more specifically, regarding the rich degree of the air-fuel ratio of the rich cylinder, the purge gas amount is set as described above during the sulfur poisoning recovery control, and the vapor concentration in the purge gas is set as the vapor concentration in the purge gas. When the gas concentration is higher than the predetermined concentration, the purge gas amount is set to be small, and when the vapor concentration in the purge gas is lower than the predetermined concentration, the purge gas amount is set to be large, or the higher the vapor concentration in the purge gas is, the smaller the purge gas amount is. And Alternatively, during normal stoichiometric control, when the purge gas amount is set according to the engine operating state (especially the engine speed and required torque), the vapor concentration in the purge gas is lower than the predetermined concentration. As in the normal stoichiometric control, the purge gas amount set according to the engine operating state is used as the purge gas amount during the sulfur poisoning recovery control, and when the vapor concentration in the purge gas is higher than the predetermined concentration, the sulfur poisoning recovery is performed. The amount of purge gas being controlled is smaller than the set purge gas amount, or the amount of purge gas under sulfur poisoning recovery control is smaller than the set purge gas amount as the vapor concentration in the purge gas is higher And

  FIG. 7 shows an example of a routine for controlling the purge control valve 37 according to the second embodiment. In the routine of FIG. 7, first, at step 20, it is determined whether or not execution of sulfur poisoning recovery control is requested. Here, if execution of sulfur poisoning recovery control is not requested, the routine ends as it is. On the other hand, when the execution of the sulfur poisoning recovery control is requested, in step 21, the rich degree of the air-fuel ratio of the rich cylinder is detected. Next, in step 22, the purge rate is set based on the rich degree detected in step 21 as described in connection with the second embodiment. In step 23, the opening degree of the purge control valve 37 is controlled so that the purge rate set in step 22 is achieved.

  Next, a third embodiment of the control of the purge control valve 37 during the sulfur poisoning recovery control will be described. In the present embodiment, the purge rate set for the normal stoichiometric control according to the engine operating state is set as the purge rate during the sulfur poisoning recovery control, and the purge control valve 37 is set so that the purge rate thus set is achieved. To control the opening degree. In this embodiment, in addition to this, during the sulfur poisoning recovery control, the fuel injection amount of each cylinder is corrected in accordance with the vapor concentration in the purge gas obtained during the normal stoichiometric control. More specifically, the vapor amount (that is, the fuel amount) caused by the purge gas to each cylinder is estimated from the vapor concentration in the purge gas, and the fuel injection amount of the rich cylinder is reduced by, for example, the amount of vapor provided to the rich cylinder. In addition, the fuel injection amount of the lean cylinder (cylinder that discharges the exhaust gas having the lean air-fuel ratio) is also reduced so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 becomes a predetermined air-fuel ratio (particularly, the stoichiometric air-fuel ratio). .

  Of course, instead of doing this, the fuel injection amount of the rich cylinder and the fuel injection amount of the lean cylinder may be reduced by the amount of vapor provided to each cylinder.

  As described above, it is also advantageous from the viewpoint of suppressing the occurrence of misfire in the rich cylinder to correct the fuel injection amount of the rich cylinder during the sulfur poisoning recovery control according to the vapor concentration in the purge gas. That is, in this embodiment, when the vapor concentration in the purge gas is high, that is, when the amount of vapor supplied to the rich cylinder is expected to be large, the fuel injection amount of the rich cylinder is reduced and the fuel in the rich cylinder is reduced. The amount is reduced. For this reason, generation | occurrence | production of the misfire in a rich cylinder is suppressed more reliably.

  FIG. 8 shows an example of a routine for controlling the purge control valve 37 according to the third embodiment. In the routine of FIG. 8, first, at step 30, it is determined whether or not execution of sulfur poisoning recovery control is requested. Here, if execution of sulfur poisoning recovery control is not requested, the routine ends as it is. On the other hand, when the execution of the sulfur poisoning recovery control is requested, in step 31, the vapor concentration in the purge gas obtained during the normal stoichiometric control is read. Next, in step 32, based on the vapor concentration read in step 33, the rich degree of the air-fuel ratio of the rich cylinder is calculated as described in relation to the third embodiment. Next, at step 33, the lean degree of the air-fuel ratio of the lean cylinder is controlled as described in relation to the third embodiment. Next, at step 34, the purge rate is set as described in connection with the third embodiment described above. In step 35, the opening degree of the purge control valve 37 is controlled so that the purge rate set in step 34 is achieved.

  Next, a fourth embodiment of the control of the purge control valve 37 during the sulfur poisoning recovery control will be described. In the present embodiment, when execution of the sulfur poisoning recovery control is requested, if the vapor concentration in the purge gas obtained during the normal stoichiometric control is higher than a predetermined concentration, the execution of the sulfur poisoning recovery control is prohibited. Then, the control being performed at that time, for example, the normal stoichiometric control is continued. When the vapor concentration in the purge gas becomes lower than the predetermined concentration, the execution of the sulfur poisoning recovery control is permitted.

  When the execution of the sulfur poisoning recovery control is prohibited, the opening of the purge control valve 37 is made larger than the normally set opening so that the vapor concentration in the purge gas becomes lower than the predetermined concentration at an early stage. It may be. According to this, execution of prohibited sulfur poisoning recovery control is permitted early.

  Further, when the sulfur poisoning recovery control is permitted and the sulfur poisoning recovery control is performed, the purge control valve 37 in any of the above-described embodiments is controlled.

  Thus, prohibiting the execution of sulfur poisoning recovery control when the vapor concentration in the purge gas is high is advantageous from the viewpoint of suppressing the occurrence of misfire in the rich cylinder. That is, in this embodiment, when the vapor concentration in the purge gas is high, that is, when the amount of vapor supplied to the rich cylinder is large and the amount of fuel in the rich cylinder is expected to increase, the sulfur poisoning recovery control is performed. Execution itself is prohibited. For this reason, misfire does not occur in the rich cylinder.

  FIG. 9 shows an example of a routine for controlling the purge control valve 37 according to the fourth embodiment. In the routine of FIG. 9, first, at step 40, it is judged if execution of the sulfur poisoning recovery control is requested. Here, if execution of sulfur poisoning recovery control is not requested, the routine ends as it is. On the other hand, when execution of the sulfur poisoning recovery control is requested, in step 41, the vapor concentration in the purge gas obtained during the normal stoichiometric control is read. Next, in step 42, it is determined whether or not the vapor concentration read in step 41 is lower than a predetermined concentration. Here, when the vapor concentration is equal to or higher than the predetermined concentration, step 42 is repeated. As a result, execution of sulfur poisoning recovery control is prohibited. On the other hand, if it is determined in step 42 that the vapor concentration is lower than the predetermined concentration, the purge rate is set in step 43 as described in connection with the fourth embodiment described above. In step 44, the opening degree of the purge control valve 37 is controlled so that the purge rate set in step 43 is achieved.

  In the above description, an example in which the present invention is applied when four cylinders are divided into two cylinder groups has been described. However, the present invention can also be applied when a plurality of cylinders are divided into two or more cylinder groups. It is.

It is the figure which showed an example of the internal combustion engine provided with the exhaust gas purification device of this invention. It is the figure which showed the purification characteristic of a three-way catalyst. It is the figure which showed the output characteristic of the linear air fuel ratio sensor. O ₂ is a graph showing the output characteristics of the sensor. 6 is a map used for setting a purge rate R during normal stoichiometric control according to an engine speed N and a required torque T. It is a figure which shows an example of the routine which controls a purge control valve according to 1st Embodiment. It is a figure which shows an example of the routine which controls a purge control valve according to 2nd Embodiment. It is a figure which shows an example of the routine which controls a purge control valve according to 3rd Embodiment. It is a figure which shows an example of the routine which controls a purge control valve according to 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 4 Intake pipe 5,6 Exhaust branch pipe 7 Exhaust pipe 8,9 Three way catalyst 10 NOx catalyst 11-14 Air fuel ratio sensor 21-24 Fuel injection valve 30 Fuel tank 32 Charcoal canister 36 Throttle valve 37 Purge control valve

Claims (12)

  An internal combustion engine comprising a plurality of cylinders, divided into at least two cylinder groups, each connected to an exhaust branch pipe and connected to one common exhaust pipe by joining the exhaust branch pipes downstream. An exhaust purification device for an engine, wherein a NOx catalyst is disposed in the common exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, exhaust gas having a rich air-fuel ratio is discharged from one cylinder group, In the exhaust gas purification apparatus that performs control to discharge the lean air-fuel ratio exhaust gas from the other cylinder group, during the sulfur poisoning recovery control, when the gas containing the vapor is purged to the intake pipe as the purge gas, the vapor in the purge gas An exhaust emission control device that controls the amount of purge gas in accordance with the concentration or the ratio of the amount of purge gas to the amount of fresh air flowing in the intake pipe.   During the sulfur poisoning recovery control, when purging the gas containing vapor into the intake pipe as a purge gas, if the vapor concentration in the purge gas is higher than a predetermined concentration, the purge gas amount is reduced or a new gas flowing in the intake pipe The exhaust emission control device according to claim 1, wherein the ratio of the purge gas amount to the air amount is reduced.   When purging gas containing vapor as purge gas into the intake pipe during sulfur poisoning recovery control, the higher the vapor concentration in the purge gas, the smaller the purge gas quantity or the ratio of the purge gas quantity to the amount of fresh air flowing in the intake pipe The exhaust emission control device according to claim 1, wherein   An internal combustion engine comprising a plurality of cylinders, divided into at least two cylinder groups, each connected to an exhaust branch pipe and connected to one common exhaust pipe by joining the exhaust branch pipes downstream. An exhaust purification device for an engine, wherein a NOx catalyst is disposed in the common exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, exhaust gas having a rich air-fuel ratio is discharged from one cylinder group, In the exhaust purification device that performs control to exhaust the exhaust gas having a lean air-fuel ratio from the other cylinder group, when the gas containing vapor is purged to the intake pipe as a purge gas during the sulfur poisoning recovery control, the rich air-fuel ratio is reduced. When the richness of the air-fuel ratio of the cylinder that exhausts the exhaust gas is larger than a predetermined richness, the purge gas amount is reduced or the amount of fresh air flowing in the intake pipe is reduced. Exhaust gas purification apparatus characterized by reducing the proportion of Jigasu amount.   During the sulfur poisoning recovery control, when purging the gas containing vapor into the intake pipe as a purge gas, if the vapor concentration in the purge gas is higher than a predetermined concentration, the purge gas amount is reduced or a new gas flowing in the intake pipe The exhaust emission control device according to claim 4, wherein the ratio of the purge gas amount to the air amount is reduced.   An internal combustion engine comprising a plurality of cylinders, divided into at least two cylinder groups, each connected to an exhaust branch pipe and connected to one common exhaust pipe by joining the exhaust branch pipes downstream. An exhaust purification device for an engine, wherein a NOx catalyst is disposed in the common exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, exhaust gas having a rich air-fuel ratio is discharged from one cylinder group, In the exhaust purification device that performs control to exhaust the exhaust gas having a lean air-fuel ratio from the other cylinder group, when the gas containing vapor is purged to the intake pipe as a purge gas during the sulfur poisoning recovery control, the rich air-fuel ratio is reduced. The larger the richness of the air-fuel ratio of the cylinder that exhausts exhaust gas, the smaller the purge gas amount or the smaller the ratio of the purge gas amount to the fresh air amount flowing in the intake pipe Exhaust gas purification apparatus according to claim.   When purging gas containing vapor as purge gas into the intake pipe during sulfur poisoning recovery control, the higher the vapor concentration in the purge gas, the smaller the purge gas quantity or the ratio of the purge gas quantity to the amount of fresh air flowing in the intake pipe The exhaust emission control device according to claim 6, wherein   An internal combustion engine comprising a plurality of cylinders, divided into at least two cylinder groups, each connected to an exhaust branch pipe and connected to one common exhaust pipe by joining the exhaust branch pipes downstream. An exhaust purification device for an engine, wherein a NOx catalyst is disposed in the common exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, exhaust gas having a rich air-fuel ratio is discharged from one cylinder group, In the exhaust gas purification apparatus that performs control to discharge the lean air-fuel ratio exhaust gas from the other cylinder group, during the sulfur poisoning recovery control, when the gas containing the vapor is purged to the intake pipe as the purge gas, the vapor in the purge gas An exhaust emission control device that controls the air-fuel ratio of each cylinder in accordance with the concentration.   The air-fuel ratio of the cylinder that exhausts the rich air-fuel ratio exhaust gas when the gas containing the vapor is purged to the intake pipe as a purge gas during the recovery from sulfur poisoning and the vapor concentration in the purge gas is higher than a predetermined concentration 9. The exhaust emission control device according to claim 8, wherein the richness of the cylinder is reduced and the leanness of the air-fuel ratio of the cylinder that discharges the exhaust gas of lean air-fuel ratio is increased.   During the sulfur poisoning recovery, when the gas containing vapor is purged into the intake pipe as a purge gas, the higher the vapor concentration in the purge gas, the smaller the air-fuel ratio richness of the cylinder that exhausts the rich air-fuel ratio exhaust gas. 9. The exhaust emission control device according to claim 8, wherein the lean degree of the air-fuel ratio of the cylinder that discharges the exhaust gas having a lean air-fuel ratio is increased.   An internal combustion engine comprising a plurality of cylinders, divided into at least two cylinder groups, each connected to an exhaust branch pipe and connected to one common exhaust pipe by joining the exhaust branch pipes downstream. An exhaust purification device for an engine, wherein a NOx catalyst is disposed in the common exhaust pipe, and as a sulfur poisoning recovery control of the NOx catalyst, exhaust gas having a rich air-fuel ratio is discharged from one cylinder group, In the exhaust purification apparatus that performs control to discharge the lean air-fuel ratio exhaust gas from the other cylinder group, the vapor concentration in the purge gas when the gas containing vapor is purged to the intake pipe as the purge gas is a predetermined concentration An exhaust emission control device that prohibits execution of sulfur poisoning recovery control when higher than that.   Whether the sulfur poisoning recovery control should be prohibited and the purge gas amount increased when the vapor concentration in the purge gas is higher than a predetermined concentration when the gas containing vapor is purged into the intake pipe as the purge gas Alternatively, the ratio of the purge gas amount with respect to the amount of fresh air flowing through the intake pipe is increased.

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